The series is set in the mid-80s, but the phone box that Vincent uses towards the end of the episode is a design that didn't exist until 1991.
When Vincent is calling Joe from a phone box outside Southend Municipal Airport (now London Southend Airport), the BT logo on the side of the box was first used in 1991, 6 years after the scene takes place. The logo should be a yellow T inside a yellow circle.